The most interesting thing today in the French Open tennis championships was a chaotic third set between two big men of similar styles and diametrically opposite temperaments, Stan Smith and Dick Crealy.

Overrall, their match was not particularly memorable. Smith, the Wimbledon and U.S. Open champion who has never reached the semi-finals on the slow red clay of Stade Roland Garros, won easily, 7-6, 6-4, 6-2, after breaking Crealy when he served for the first set at 5-3, 30-0.

Smith thus moved into the second round, along with Adriano Panatta, the defending champion who beat Patrice Beust, 7-5, 6-4, 5-7, 6-2; and fifth-seeded Raul Ramirez, who cruised past Georges Goven, 6-4, 6-1, 7-5.

What gave the Smith match character was the tempest that swirled around Crealy, an engaging but incurably spacey 6-foot-5 Australian with a gait like Ichabod Crane, limbs like an octopus, an expressive face dominated by a great expanse of teeth and a tendency to go round the bend when the game becomes too exasperating.

It did today in the third set of a match Crealy knew he had let slip away. His mind had drifted into a world of fits own and he couldn't bring it back. He wasn't getting any breaks. It was raining. Thousands of schoolchildren in the "youth day" crowd were howling. The wind was blowing, and so was Crealy.

He ambled around the court, muttering and sputtering. He talked softly to himself. He yelled loudly to the heavens. He buried his head in his hands. Agony darted across his face, frustration was in very gesture.

His brown hair was soaked, matted, disheveled. His shirttail was out. Nerve endings were frayed and showing. Crealy was flailing at every ball, hitting a million-miles-an-hour winner or the back fence. He was disarray personified, right down to the blue shirt and shorts, that didn't quite match.

When thus distracted, Crealy is like a man constructed of tighly stretched rubber bands that snap one by one. Because there is a certain unique style and humor to his distintegration, it is a fascinating and amusing spectacle. Word spread throughout the players' dining and dressing room - "Creals is gone" - and his colleagues gathered around TV monitors. At 1-1 in the third set, Crealy got a bad call from an elderly linesman. He went berserk. "No, no, not that one, he screamed in his piercing Australian inflection. For awhile he looked like he would walk off court as he once did in the German championships, claiming "cramp in the brain."

"It was all too bloody much for me, "Crealy said later, after he had thrown his racket against a sidewall, threatened to smash another, blasted a first serve into the stands, and gotten 10,000 Frenchman screaming at hime for an eruption that was more comical than nasty.

"I get those days. Sometimes I'm playing well, I'm dangerous, and sometimes I'm very bad. I couldn't get going. I was out of it, I didn't have the touch.

"I got aggravated with the calls and the rain. That guy called the ball out. . . He couldn't see. He's 100 years old. It's the same story every year. When I'm 100, I'm not going to be a linesman.

"I couldn't stand it anymore. A fellow's allowed to vent a little frustration, isn't he? The crowd didn't mind. They love a little hissing and booing. They're excitable people.

"So I whistled back at them. No big deal. They're like Australians. I've played some good matches here, I've gotten good support, especially the year we won the doubles (1974, Crealy and Onny Parun)."

Smith, for his part, played well and remained impassive as always, tall and dignified. He seemed to sympathize with Crealy.

"Later in the third set he tried to give me a point on a bad call against me, and they whistled at him again, not realizing he was just trying to be a nice guy," the 6-foot-4 Californian said.

"He's tough to play against because he's so streaky and unpredictable," added Smith, who approached and volleyed well, especially on the forehand, but was inconsistent in baseline rallies. "It got to be a really strange atmosphere out there. It was tough to concentrate. But he's more volatile than I am."

And mustard is hotter than ice cream.

The best match of the day was one resumed after interruption by a thunderstorm at nightfall on Tuesday. Australian Phil Dent, who upset Ilie Nastase at Rome last week, beat 1973 runner-up Nikki Pilic, 1-6, 4-6, 7-6, 6-4, 6-4.

Pilic, dispirited after blowing his two-set lead, made a brief revival from 0-4 in the final set after cutting a ball with such exaggerated spin that it went over the net, bit into the clay, and bounced back over on Pilic's side before Dent could get to it.

In another match resumed from the previous evening, Fred McNair IV of Chevy Chase, Md., rallied froma a two-set deficit but then lost to German Davis Cuper Jurgen Fassbender, 6-4, 7-6, 3-6, 1-6, 6-4.

Under a memorandum of agreement to be signed with the city, the USTA guarantees to spend at least $5 million modernizing and rehabilitating the existing Louis Armstrong Stadium, about five miles from the West Side tennis club at Forest Hills. City Hall said the arrangement would permit the transfer of the U.S. Open to the new facility beginning in 1978.